Mycobacterium bovis Tuberculosis May be Spread Through the Air

The Centers for Disease Control and Prevention has released a paper published in the Morbidity and Mortality Weekly Report that brings up a possible risk for people who consume imported raw milk products or who eat raw milk products while in other countries. Mycobacterium bovis, a zoonotic pathogen of cattle, causes tuberculosis in people who eat unpasteurized contaminated dairy products in or imported from countries with affected cattle herds. That’s bad enough, but scientists now believe that this illness can be transmitted person-to-person through the air. This investigation strengthens the evidence for person-to-person airborne transmission of M. bovis infections.

In April 2014, a man in Nebraska who was born in Mexico was diagnosed with extensive pulmonary tuberculosis caused by M. bovis after he was sick for three months with cough and fever. He did report frequent consumption of raw milk when he lived in Mexico.

Four months later, a U.S.-born Hispanic girl from a nearby town was also diagnosed with the infection. She had never traveled outside of the United States and was unaware of any consumption of dairy products from Mexico. Whole genome sequencing of the isolates from the two patients were “nearly indistinguishable.” The only social connection between the two patients was attendance at the same church.

Contacts of those two patients were then examined. Those exams of 181 people yielded 77 who needed retesting to confirm infection. Of those people, 10 had close exposure to either patient, 28 were exposed to one or both of the patients at church, and one was exposed to the girl at school. Skin tests and IGRA tests were conducted on the contacts. Anyone with a positive skin tests was scheduled for retesting.

Of the 77 people who were retested, six had latent infections when they were examined two months later. None of those sickened could recall consuming unpasteurized dairy products from Mexico, and none had active TB at the initial or secondary examinations. No one who tested positive had traveled outside the U.S. None of the infected contacts had active TB disease. The report states that locally produced raw milk products were unlikely to be contaminated with M. bovis.

The timing of the girl’s illness suggest that she acquired the infection from the man born in Mexico. The report adds to the evidence for airborne person-to-person spread of M. bovis, and recommends that doctors who see patients presenting with M. bovis TB ask about consumption of unpasteurized dairy products imported from or consumed in other countries.